1911.] 



NATURAL SCIENCES OF PHILADELPHIA. 



151 



The two extremes of form are so different that they may well represent 

 two successive migration waves, but the high-spire forms predominate. 

 Two of the shells were probably semi-fossil (Plate XI, fig. 1), but their 

 index is near the average for the group and they were not larger than 

 many taken at this colony. In actual size the two flat shells above 

 mentioned are probably as large as many Somerset normal forms, 

 measuring, height 21 mm. by width 46 mm. and 23 x 42^ mm., respect- 

 ively, with indices of .553 and .541. This colony was at a lower 

 level above sea than any other examined in this region ; it is, as noted 

 above, the most northerly point of the second migration line which 

 seems to be indicated in the specimens of this collection. The dimen- 

 sions of the entire 18 specimens are given in the diagram, fig. 11, but, 



Fig. 11. — Kendal Road. 



as will be seen, they are rather scattered. Average dimensions by 

 whorls were measured for a small selected series of these specimens, 

 they show that up to 2 whorls the diameter is equal or rather more 

 than that of the normal Somerset forms, at whorl 3 about the same 

 size and at whorls 4 and 5 somewhat smaller. When fully grown 

 they are about the diameter of the Somerset hill-top forms. The 

 index is higher than that of any of the Somerset forms, though near 

 that of the Somerset Road forms. The average dimensions of the 

 adult shell may be stated as, height 23.1 mm. ; width 42 mm. ; index .55 ; 

 mean divergence in the flat forms 130°, in the forms with high spire 95°. 

 These forms are mostly one-toothed, 13 of the series had only the 

 outer tooth and the other 5 had only a rudimentary inner tooth in 

 addition. All have the umbilicus completely closed by an expansion 

 of the lip. 



